The present invention relates to small implantable medical devices, and in particular to lead assemblies for such devices. Such small devices are easily implantable, and provide stimulation and/or sensing functions. The lead assembly is removably electrically connectable to an existing electrode of the device, thereby providing means to stimulate tissue, or sense physiological parameters, at some distance from the device.
Implantable electrical stimulation devices have proven therapeutic in a wide variety of diseases and disorders. Pacemakers and Implantable Cardiac Defibrillators (ICDs) have proven highly effective in the treatment of a number of cardiac conditions (e.g., arrhythmias). Spinal Cord Stimulation (SCS) systems have long been accepted as a therapeutic modality for the treatment of chronic pain syndromes. Deep Brain Stimulation (DBS) has been applied in areas such as movement disorders. Functional Electrical Stimulation (FES) systems, such as the Freehand system by NeuroControl Corporation (Cleveland, Ohio), have been applied to restore some functionality to paralyzed extremities in spinal cord injury patients.
Current implantable electrical stimulation systems typically consist of a leaded system wherein the electrodes are on a lead and are separate from but connected to a System Control Unit (SCU) that contains the power source and the stimulation electronics. A number of these systems have the advantage of having fixation devices for the electrodes, so that the electrodes remain proximal to or even attached to their target sites of stimulation. For example, some pacemaker electrode leads have tines that act as barbs to hook into the tissue, thereby anchoring the electrodes in place. As another example, the electrode used in the Neuro Cybernetic Prosthesis (NCP®) manufactured by Cyberonics (Houston, Tex.) is a helical electrode that is wound around the vagus nerve in order to remain attached to its stimulation target. In addition, several companies and research institutions, such as Neuro Stream Technologies, Inc. (Anmore, British Columbia, Canada) are investigating cuff electrodes, which wrap around the nerve like a cuff, thereby fixing an electrode(s) in close approximation to a nerve.
A microminiature electrical stimulator known as the BION® microstimulator has been developed to overcome some of the disadvantages of a large SCU-based (a.k.a. IPG-based) system. The BION microstimulator is a leadless device, wherein the SCU and the electrodes have been combined into a single microminiature package. The current embodiment of the BION stimulator is a cylinder that is approximately 3 mm in diameter and between about 2 and 3 cm in length. This form factor allows the BION microstimulator to be implanted with relative ease and rapidity, e.g., via endoscopic or laparoscopic techniques. Thus, the BION microstimulator may easily be implanted subcutaneously, and in such a configuration it is unlikely to demonstrate problems with cosmesis or erosion.
A known microminiature electrical stimulator, a microstimulator, is described in U.S. Pat. No. 5,193,539 issued May 16, 1993 for “Implantable Microstimulator.” A method for manufacturing the microstimulator is described in U.S. Pat. No. 5,193,540 issued May 16, 1993 for “Structure and Method of Manufacturing of an Implantable Microstimulator.” Further teaching is included in U.S. Pat. No. 5,324,316 issued Jun. 28, 1994 for “Implantable Microstimulator.” The '539, '540, and '316 patents are incorporated herein by reference.
In some applications, e.g., pudendal nerve stimulation for the treatment of incontinence, the leadless BION microstimulator system has proven sufficient. In such applications, the BION microstimulator is surgically placed near an easily identifiable landmark(s), e.g., the pudendal canal. Additionally, in such applications the stimulator is surrounded by soft tissue and is not embedded in or located very close to large muscles or other structures that may demonstrate significant motion or varying pressure.
However, for other applications, a leadless BION microstimulator may prove insufficient or inappropriate. For example, it may be desirable to implant a BION stimulator close to the skin, to facilitate power and/or data transfer, and/or to facilitate removal and/or replacement, while a lead assembly removably attached to the BION device may stay in place, with the electrode(s) positioned for appropriate tissue stimulation, possibly deep within the body.
What is needed are lead assemblies for microdevices which facilitate removal and/or replacement of the microdevice by reducing or eliminating the ingress of fluids into the assemblies.